Float-type flowmeters are well known in the prior art, as is indicated by U.S. Pat. No. 2,993,374 to Dwyer et al, issued July, 25th, 1961. When positioned for operation, such flowmeters usually include a float chamber which extends in a substantially vertical direction between a first, bottom, end and a second, top, end. The float chamber is shaped so its cross-sectional area in the horizontal plane increases from its bottom end toward its top end. The flowmeter includes an inlet opening which is positioned to receive a portion of the flow of fluid which is to be sampled or measured. It also includes means for channeling the sampled portion of the flow received by the inlet opening into the bottom end of the float chamber. An outlet opening is provided for releasing at least a part of the sampled flow from the top end of the chamber.
A float is located in the float chamber. It is designed to move between the bottom and top ends of the chamber. The float is pulled by gravity toward the bottom end and is pushed toward the top end by the sampled flow. It will tend to reach an equilibrium position when the force of gravity pushing the float down equals the force of the net pressure of the sampled flow pushing the float up. The net pressure pushing up on the float is a function of the difference between the fluid pressure below the float pushing up and that above the float pushing down. This difference in pressure varies as a function of the cross-sectional area which the sampled flow has to flow around the float. Since the cross-sectional area of the chamber increases as the float moves up, the cross-sectional area for the fluid to flow around the float also increases as the float moves up the chamber, decreasing the net pressure pushing up on the float for a given volume of fluid flow in the chamber. Thus the float tends to find an equilibrium position which indicates the volume of flow being measured.
Usually such flow chambers have transparent sides so that the position of the float can be seen by a user of the flowmeter, and usually the chamber has calibration marks placed on its exterior so that the position of the float can be read as indicating a given calibrated flow velocity.
Such float-type flowmeters are often used to measure a flow which travels in a fixed direction, such as the flow of fluids through pipes. But as the Dwyer patent cited above indicates, such flowmeters have been used as wind meters. They have many benefits when used as wind meters, such as the fact that they can be relatively small, light, and inexpensive, thus making them ideal for portable wind meters. However, such prior art float-type wind meters require the person using them to hold them and point their inlet opening into the wind in order to function properly. Such hand held wind measuring devices are often impractical for sailboats because sailors are often occupied with attending to various manual operations, such as manning the tiller and adjusting the sheets. These operations become even more crucial in racing, in which reaching for a hand-held device and then adjusting its position to point into the wind can be impractical. Also , a hand-held device, when not in use, can become a loose item in a heeling sailboat, making it difficult to keep at hand and posing a hazard if it gets under foot.
Some prior art float flowmeters, such as that disclosed in the Dwyer patent cited above, include means for enabling the device to give readings of wind velocity over an extended range of wind speeds. The Dwyer device does this by having two outlet openings, one of which is relatively large, and one of which is relatively small. If the device is measuring relatively low wind speeds, both opening are left open, allowing a larger volume of air to flow up through the float chamber. But if the user of the flowmeter wants to measure higher wind speeds, he or she puts his or her finger on the large outlet opening, leaving only the smaller opening to release air from the float chamber. This greatly reduces the air flowing up the float chamber, and allows much higher wind speeds to be measured. This use of two separate openings at the top end of the flow tube does let the wind meter measure wind speeds over a broad range of wind speeds, but it requires the user to cover up the large opening to measure high winds.